The viscosity of oils of lubricating viscosity is generally dependent upon temperature. As the temperature of the oil is increased, the viscosity usually decreases and as the temperature is reduced, the viscosity usually increases.
The function of a viscosity improver is to reduce the extent of the decrease in viscosity as the temperature is raised or to reduce the extent of the increase in viscosity as the temperature is lowered, or both. Thus, a viscosity improver ameliorates the change of viscosity of an oil containing it with change in temperature. The fluidity characteristics of the oil are improved.
Viscosity improvers are usually polymeric materials and are often referred to as viscosity index improvers. Ethylene-alpha olefin-diene copolymers are a well known member of the group of polymeric materials which find use as viscosity improvers for lubricating oils.
A wide variety of ethylene-alpha olefin-diene copolymers are available. Many of these copolymers, while eminently useful per se as materials which can be fabricated into a wide variety of products, do not possess properties which render them useful as viscosity improving additives for lubricating oils. A specific property of many such polymers that renders them unsuitable for use as viscosity improvers for lubricants is their extremely high molecular weight. Polymers of extremely high molecular weight are difficult to dissolve in a diluent, requiring excessive time to dissolve. While such polymers may provide desired kinematic viscosities at 100.degree. C. at very low treating rates, they are very shear unstable, making the formulation of stay-in-grade lubricants virtually impossible, or formulations must contain sufficient polymer such that initial viscosity exceeds the desired grade so that the lubricant may meet minimum desired viscosity after shearing.
High molecular weight polymers often are susceptible to extreme shearing during use. Such shearing results in substantial loss of lubricating viscosity which can lead to increased engine wear and reduced engine life.
It has been found that many such high molecular weight polymers which are unsuitable for use as viscosity improvers for lubricating oil compositions may be modified by subjecting them to shearing. Shearing of polymers causes a reduction in molecular weight to levels which render them suitable for use as viscosity improvers for lubricating oils. Nevertheless, shearing of the polymers, particularly shearing conducted in solution, may create additional problems such as the formation of insoluble gelatinous or pituitous gels.
U.S. Pat. No. 3,772,169 relates to handling problems associated with oil solutions of hydrogenated butadiene-styrene copolymers. It is noted that at high concentration of polymer in oil (e.g., 20-25% weight) restricted flow is encountered, while at lower concentrations (less than 20 weight percent, e.g., 10 weight percent), on storage the polymer-oil concentrates tend to form a gel. The patent teaches that the addition of additional polymer compounds eliminates or significantly reduces gelation of the concentrates.
U.S. Pat. No. 2,510,808 relates to synthetic polymers, particularly curable synthetic polymers of rubbery character and especially to a means for adjusting molecular weight and plasticity of rubbery polymers for maximum ease of processing. Milling is one means for adjusting the molecular weight of such polymers. In particular, polymers of isobutylene with polyolefins such as butadiene or isoprene, especially those of molecular weight in excess of 70,000, are difficult to mill because of low fluidity and high elasticity. This problem is addressed by treating the polymer with an aliphatic mercaptan and milling at elevated temperature until the desired viscosity is attained.
U.S. Pat. No. 2,466,301 relates to a method of plasticizing a rubbery copolymer having unsaturation greater than 0.5 mole percent and prepared by reacting isobutylene with a conjugated di-olefin having 4-6 carbon atoms in the molecule, which method comprises treating said polymer with an aryl mercaptan as a plasticizer. This treatment improves mechanical processing of the polymers.
U.S. Pat. No. 4,110,235 relates to improving the color and viscosity stability of ethylene-alpha olefin copolymer viscosity improvers for mineral oil lubricants. This patent teaches the use of N,N'-bis (2-OH-5-alkylbenzyl)-.alpha.-.OMEGA.-diamino alkanes or metal salts thereof as viscosity and color stabilizers in compositions containing ethylene-alpha olefin copolymers.
In U.S. Pat. No. 4,933,099 it is noted that ethylene terpolymers which contain dienes, e.g., 5-vinyl-2-norbornene or ethylene tetrapolymers containing both 1,4-hexadiene and 2,5-norbornadiene are not suitable for mechanical degradation as by mastication in the presence of air or oxygen whereby oxidation occurs since this technique produces excessive amounts of polymeric gel particles which are oil insoluble. As a solution, the patent relates to the use of ethylene copolymers also containing a C.sub.3 to C.sub.18 higher alpha olefin and from 1-25 weight percent of alkyl norbornene having from 8-28 carbon atoms.
U.S. Pat. No. 4,873,005 relates to extrusion lubricating compositions for vinyl halide resins comprising mixtures of hydrocarbon wax, group II or lead salts of fatty acids and organic mercaptans.
U.S. Pat. No. 5,270,369 relates to a composition comprising a polyolefin and a hydroxyl amine having improved clarity and viscosity. The patent further describes a method of reducing viscosity and improving clarity of polyolefins wherein the process comprises visbreaking in the presence of a hydroxyl amine.
As noted above, shearing may be intentional, i.e., when it is desired to reduce the molecular weight of a polymer. Shearing may take place during use, e.g., when the polymer is present in a lubricating oil composition employed in an environment where it is subjected to shear and elevated temperature. In either event, the formation of insoluble gel-like components upon shearing is undesirable.
Accordingly, it is desirable to provide compositions that reduce the extent of loss of viscosity of lubricating oil compositions as temperatures are increased.
An object of this invention is to provide novel viscosity improvers lubricating oil compositions.
Another object is to provide a means for utilizing a broad range of available polymeric compositions for use as viscosity improvers for lubricating oil compositions.
A further object is to provide a method for adjusting the molecular weight of polymers such that they may be used as viscosity improvers for lubricating oil compositions without the development of undesirable side effects.
A particular object of this invention is to provide a polymer containing composition which, on shearing, does not develop, or develops only a minor, insignificant amount, of oil-insoluble gelatinous particles.
A further object is to provide a method for preventing or reducing the tendency of polymers to form undesirable gelatinous particles when the polymers are sheared in solution.
Another object is to provide lubricating oil compositions containing as an additive polymeric compositions which are resistant to formation of undesirable gelatinous particles on shearing.
Yet another object is to provide lubricating oil compositions containing polymeric compositions which have been subjected to shearing but which do not contain undesirable gelatinous particles.
Other objects will in part be obvious in view of this disclosure and will in part appear hereinafter.